Revert "SERVER-8710 check balancer is stopped before upgrading"

This reverts commit e57f5d32d93cd23971cadfcdb93a4b9f07a0ef5a.
SERVER-8710 check balancer is stopped before upgrading to nonzero config version
SERVER-8761 ignore non-shard connections in conn pool test
SREVER-8780 turn off balancer in unit tests for config upgrade
SERVER-8781 buildbot sharding_migrateBigObject better error message when balancing fails due to I/O problems
SERVER-8760 DBClientReplicaSet::slaveConn returns connection to primary
SERVER-8758 : make IndexSet a set rather than a vector
SERVER-8758 - don't go past StringData end since it might not be null terminated
            - fix $ handling in middle of string
SERVER-8758 - IndexSet fix for ab vs a
SERVER-8685: mongorestore oplogLimit fixes
SERVER-7718: JS Timestamp constructor now in seconds (not millis anymore)
SERVER-8594 fix clearTmpCollections for collections with indexes
SERVER-8488 Visual Studio -- enable intrinsics in debug builds
SERVER-7718: more test cleanup related to Timestamp
SERVER-8685 Fix gcc compile
SERVER-8734 use a recursive mutex to work around OpenSSL deadlock
buildbot version2.js use assert.eq to make it simpler to figure out what went wrong
SERVER-8769 Track inserts on mongos for serverStatus().opcounters
SERVER-8691 better error messages when setsockopt fails on Windows
SERVER-8734  do not crash on SSL connection failure